Ghost Immobiliser vs Relay Immobiliser: Which Does Your Fleet Need?

Ghost immobilisers and relay immobilisers get lumped together, and a lot of what’s written about them online is just wrong. One popular claim is that a relay immobiliser is vulnerable to relay attacks because of the name. It isn’t. The two “relays” have nothing to do with each other.

Both types stop a vehicle starting. The real difference is who’s in control. A ghost immobiliser is controlled by whoever knows the PIN. A relay immobiliser can be controlled by you, from the office, without anyone touching the vehicle. For a fleet, that difference matters a lot more than which one is “more secure”.

The short answer

A ghost immobiliser makes the driver enter a PIN on the car’s existing buttons before the engine will start. It’s hidden, gives off no signal and is excellent against relay attacks and cloned keys.

A relay immobiliser cuts a circuit the engine needs, and is switched by an external signal: a driver ID tag, or a command from a connected platform. When it’s connected, it’s called a remote immobiliser, and it lets you stop a vehicle restarting from a dashboard.

Ghost is driver-controlled theft prevention. Relay is operator-controlled access. Many fleets end up wanting a bit of both.

First, clear up the “relay” confusion

A relay attack is a theft method. Thieves use two devices to boost the signal from a keyless fob inside a house so the car thinks the key is next to it. Our guide to relay attack car theft explains how it works on fleets.

A relay immobiliser gets its name from the electrical relay inside it, a switch that opens or closes a circuit. It has nothing to do with the key signal, and a relay attack doesn’t switch it off. If the immobiliser is armed, a car unlocked by a relay attack still won’t start.

How a ghost immobiliser works

A ghost immobiliser connects to the vehicle’s internal data network and blocks the engine starting until a PIN sequence is entered on buttons the car already has, things like the steering wheel controls, window switches or indicator stalk. There’s no keypad, no fob and no signal, so there’s nothing for a thief to clone, jam or intercept.

Where it’s strong: theft prevention. Relay attacks, cloned keys and OBD reprogramming all target the key, and a ghost immobiliser doesn’t care about the key.

The catch for fleets: it’s built around one PIN. On a fleet that usually means a shared code, which is only as safe as your worst habit. Every time a driver leaves, the PIN needs changing, and there’s no record of who started which car. Our ghost immobiliser guide for fleets covers how operators manage that.

How a relay immobiliser works

A relay immobiliser interrupts a circuit the engine needs to start. Instead of a PIN, it’s switched by an external signal, usually one of two things.

Driver ID tags. Each authorised driver carries a small tag. No tag, no start. That stops anyone without a tag starting the vehicle, including someone holding a spare or stolen key, and it logs which driver started which vehicle and when.

Remote commands. Wired into a connected device, the relay can be armed or released from a dashboard. That’s a remote immobiliser. If a vehicle is being used without authorisation, you can stop it being started again, wherever it is, without sending anyone out. Our immobilisers quick guide walks through the flow.

Where it’s strong: control. You decide who can start which vehicle, you can change that instantly, and you get a record of it.

The catch: it’s a physical install, so it needs a good installer who hides the wiring properly. And the remote side relies on the vehicle’s connection to receive a command, so it complements prevention rather than replacing it.

Side by side

Which one does your fleet need?

Taxi and PCO operators

If drivers own or permanently keep their vehicles, a ghost immobiliser on each car is simple and effective against theft. If you run a pool of cars across shifts, driver tags on a relay immobiliser solve the shared PIN problem and tell you who had which car overnight.

Rental and car club fleets

Relay, connected, almost every time. You need to control access booking by booking, stop a vehicle restarting if it isn’t returned or is being misused, and keep a record. Make sure your rental terms explain that vehicles can be immobilised and in what circumstances.

Dealerships

Ghost immobilisers suit high-value stock that sits on the forecourt, where theft is the main risk. Connected relay immobilisers suit demonstrators and courtesy cars that leave with customers, which we cover in tracking courtesy cars, demonstrators and test drives.

Van and logistics fleets

Driver tags on a relay immobiliser are the practical choice. They stop unauthorised use, give you a record for every start, and don’t depend on a PIN being kept secret across a depot full of drivers.

Can you fit both?

Yes, and on high-value or high-risk vehicles some operators do. The ghost immobiliser handles theft at the vehicle, the connected relay gives you remote control and a record from the office. Add a GPS tracker to cover the one thing neither stops: a vehicle lifted onto a flatbed.

A note on using remote immobilisation fairly

A fleet immobiliser should stop a vehicle starting again. It should never cut an engine while the vehicle is moving. Set out in your driver or rental terms when you’ll use it, keep a record of every time you do, and take advice before using it on vehicles that customers have on finance, where the Consumer Credit Act and FCA rules still apply. Our post on vehicle finance recovery tracking covers that side.

Frequently asked questions

What’s the difference between a ghost immobiliser and a relay immobiliser? A ghost immobiliser needs a PIN entered on the car’s own buttons before it will start. A relay immobiliser cuts a circuit and is controlled by a driver tag or a remote command. Ghost is driver-controlled, relay is operator-controlled.

Is a relay immobiliser vulnerable to relay attacks? No. The name comes from the electrical relay inside it, not the theft method. A car unlocked by a relay attack still won’t start if the immobiliser is armed.

Which is more secure, ghost or relay? Both are strong against relay attacks and cloned keys when properly fitted. The bigger difference is control. Ghost relies on the PIN staying secret. Relay lets you manage access per driver and act remotely.

Can a relay immobiliser stop a car while it’s being driven? A properly set up fleet immobiliser stops the vehicle starting again. It shouldn’t cut the engine while the vehicle is moving.

Do immobilisers reduce fleet insurance? Sometimes. It depends on the insurer and the system. Many mainstream insurers don’t formally recognise ghost immobilisers. Check with your insurer or broker before you count on a discount.

Not sure which fits your fleet? Talk to Traknova. We fit both and can tell you which makes sense for how your vehicles are used.